Farmers have in the past taken soil samples in a few selected positions in a farm field. The soil samples were analyzed to determine what plant nutrients were lower than desired for the next crop and to determine the effective hydrogen-ion concentration (pH). Chemicals were then applied to the entire field based on a few soil samples. The application of chemicals was based on an assumption that the same chemicals were needed in the entire field. Sometimes it was assumed that other fields in the same general area needed the same additives without analysis of soil samples from each of these other fields.
Many of the chemicals applied to fields today such as ammonia are made from hydrocarbons. Hydrocarbons and other chemicals based on oil are relatively expensive and will most likely become more expensive in coming years. Farmers have also learned that many chemical additives will damage crops if the concentrations are too high. A significant expense is incurred each time a chemical is applied as a liquid, a gas, a powder or as granular solids. These expenses can be reduced by applying chemicals at the same time other activities such as tillage, planting, row crop cultivation, or crop harvesting occur. However, some chemicals need to be applied when none of the above activities are appropriate.
Harvesting machines are often equipped with global positioning systems and sensors that measure crop yield, moisture content, protein content, and other factors that may be of interest. Chemical applicators with global positioning systems and application controls connected to an application controller are commercially available. These computer controlled applicators can control chemical application rates to apply the desired application rate throughout the entire area of a field and to substantially eliminate excessive chemical application in all areas of a field.
Determining the quantity of each chemical that needs to be applied to each part of a field is based on soil samples, past crop production data, and the requirements of the next crop to be planted in the field. To obtain the best data to determine the quantity of each chemical to be applied, a substantial number of soil samples taken in a predetermined distribution throughout the field need to be taken. Each soil sample obtained is identified by the location in which it was taken and the date on which the sample was obtained. The date of the sample is important because the measured quantities can change over time. Volatile chemicals may evaporate over time for example. The number of soil samples that can be obtained in a given period of time is limited by the apparatus employed to obtain each soil sample.